For years it has been speculated upon: can you transplant a ZF six speed out of a C4 into a C3 practically? Well I'm here to tell you yes you can, I did it and it wasn't that hard. The only other person I'm aware of that has done this is a cat that goes by Twin Turbo, who use to contribute here a lot, but his chassis was highly modified (Marck, if you are still checking in what do you think?). I modified nothing on my chassis. All it took was a block of aluminum, four bolts and a little imagination. Now, I don't have a rubber or polyurethane isolation block integrated with this mount, but I doubt I'll notice much vibration from the solid mount. The engine is rubber mounted. If you wanted an isolation block you would have to cut the cross member down and weld a new mounting plate in it. Follow along with the photographs and I'll explain how I did it.

Here's the stock cross member with the trans tail. Notice the bulge on the bottom of the tail shaft extension. That houses the VSS sensor.

Same thing, right side.

Same thing again, left side.

And here is all you need. A 3.25" X 2.75" X 1.125" thick block of aluminum. Socket head cap bolts were counter sunk and pressed in before relieving the block to clear the VSS. The 5.50" X 7/16" bolts go through the tail housing holes. I found the 1.125" thickness gave me the ideal 3 degrees of pinion angle.

Same thing, different view.

And here it is, all bolted up.

Left side view. Even the E-brake pulley clears.

It's a big transmission, but if my measurements are correct it should fit with very little modification to the trans tunnel and floor boards. The shiftier is 2" further back but a custom shiftier plate will take care of that.

Anybody see anything wrong here?

Or from this angle?

So there you have it, the drive train out of a 1991 C4 into a 1977 C3. I was even able to use the stock aluminum drive shaft out of the C4 with no modification!

 

very nice, thanks for sharing

Neal

 

Assuming that the Engine mounts are not solid the Engine will twist with torque So will the Transmission. .Therefore I would not want the Trans bolted solid to the Crossmember. It doesn't that much, just a Polly mount between the two should do it.

 

I am interested to see how much floor modification is necessary for this change

Kael

 

I'm also interested to know if there was a specific reason you chose to use the ZF transmission rather than a T-56. Was it that you already had the drivetrain available? Or was there another reason?

Thanks,
Kael

 

Looks good!

 

Great looking install. You didn’t mention making the tranny crossmember removable. You need to because you will never get that out with the body on it. The shift box will be sticking up through your tunnel and you will be killing yourself to twist it to get it out. Please save yourself a lot of frustration and make it removable

 

OK, first off I will probably try to find a thin piece of poly to insert between the pillow block and cross member. Don't want to stress the tail housing too much.

I'm not going to cut up the cross member because, in the rare insistence I do need to remove the trans, it is easier to just pull the engine and trans out together. The shifter lever can easily be removed from inside the car. That trans weighs 145 pounds and I don't want to have to wrestled it out from underneath. The clutch and flywheel are new, so I don't foresee that happening. Worse case scenario: I just get the saws all out.

As far as the floor is concerned, according to Twin Turbo, I should only have to cut out a place for the clutch hydrophilic slave cylinder. I took a lot of measurements before lifting the body and comparing the ZF with the T 10 and it should fit without changing anything but the shifter hole, which is centered rather than offset to the left.

So, why the ZF? I could have spent thousands of more dollars for a T 56 and still have to do as much or more modification. I purchased this L98 aluminum head, high compression engine with the ZF six speed plus all of the accessories (new alt, A/C compressor, starter, serpentine drive setup, TPI , clutch and flywheel) for $2,,000. The '91 C4 it came out of only had 90,000 miles on it. I reckon I would have spent north of $3,500 for a T 56 with the necessary conversion parts alone. Now, I don't know if you know much about this transmission, but it is know as one of the strongest overdrive manuals GM ever used. It is conservatively factory rated for 450 FPT but realistically 600. It has a very nice 2.68 first gear ratio with .75 and .50 overdrive ratios. You ought to see the size of the output shaft on these things. For far less dollars it is very comparable to the T 56. And besides, I am an old school hot rodder. That means taking what is available from the factory, the junk yard or what you have laying around and making something better from it. That is also why I purposely choose the L98 over a create motor or the ubiquitous LS engine. I would much rather see what I can engineer myself rather than buy a bunch of new parts and bolt them together, no offense to those that do.

Once I get my headers back from coating I will post pics of the whole chassis complete with drivetrian, exhaust and running gear on my build thread "Hello from Montana". Thank you for your continued support and most importantly, your observations and contributions.

 

As an owner of a 1996 Grand Sport LT4- ZF trans I can say that this is just a great driving transmission combination. I would recommend installing a B&M Ripper Shifter or one of the others available before You install the body. If You haven't already found ZFDoc.com its a great sight to learn more about them.

 

Really nice work!!! Haven't seen Marck around in forever.

Trust me- I thought -oh- everything is new -everything will work great- will be years and I'll just pull the engine out if I need to remove the transmission....

When somehow along the install the clutch line got kinked and had a pin hole leak...I modded the crossmember while the body was on- a LOT tougher... Just sayin

Richard

 

Yes, I am familiar with ZFDoc. I've poured over all of his tech info numerous times before I decided to jump with this transmission. Unfortunately, I have not been able to find an aftermarket shifter for the ZF, only the shortened sticks from Hurst of ZF Doc. I would love one if it exits, do you have such an animal? The factory shifter isn't bad, just a little long on the through.

I know what you are saying about the cross member but I would rather not re-engineer everything right now. I don't have any internal hydro lines and everything inside of the bell housing is new. To pull the engine/trans combo together only takes five inches of forward movement of the engine. The shifter box is the same height as the rest of the trans, so no hang ups there. A saws all will fix the problem if it arises and then I can build a removable center section.

 

Marck left here back near 20 years ago, and went to another forum dig it all cor vettes, and so from there to yet another, then he probably got married and gave up the hobby......

he was in Netherlands, and had a brother also on the forums.....

been a while, hope he/brother are OK......

 

Xander. They were tripletts BTW.

 

Thank you for replying to my question about why not a T-56 with a well thought out response. That is exactly the type of information I was interested in

I currently have a large lack of knowledge and am always interested in why something is done differently than what the masses are doing.

Kael

 

You bet, Kael, glad to share experience with you. I actually corresponded with Marck here a few months ago. I sent him a PM which he eventually saw and answered me back. He even gave me his phone number in the Netherlands. Very nice guy!

 

B2Bird and I would like to establish contact with him,......I missed seeing him many years ago when he and brothers? visited this side of the ocean.....please send us the numbers.....

GENE SLATER/MRVETTE......who knows, he maybe even remember me....15? years now??

 

Very interesting thread. Now that folks know that it can be done and is very affordable, I'm sure more will do it. C4 drive trains do have a lot to offer over the pre-ecu C3 systems.

 

I'm sorry Gene, but I didn't call him or keep the phone number. I have emptied my PM file since then too, so can't get it there either. You could try to send him a PM on this forum and see if he gets it. I know he is active on another Corvette site but I don't know which one.

Yes, there are still a lot of these transmissions out there. They never seem to ware out. Kinda like Ford Toploaders. The only drawback to the ZF's is that they came with a special dual mass flywheel that is no longer manufactured. I was lucky the flywheel and clutch assembly in my trans had been replaced and then very little used. It had a 1998 date stamp on it.

The reason for the dual mass design was because the ZF has more square cut gears then most transmissions which causes some vibration noise like a Muncie M22 "Rock Crusher" (thus the name). That is why they are so strong. However, both McLeod, Ram and others make a replacement single mass flywheel and clutch that fits the ZF setup and is reported to be pretty quiet. I wouldn't be concerned with a little gear noise myself. My Toploader in the Fairlane whines too. And Chevy guys would kill for a Rock Crusher.

Another feature I like about the ZF is the external hydraulic clutch slave cylinder. It is a pull type and doesn't interfere with headers or anything else. Both the slave cylinder and master cylinders are readily available for cheap. You may also have noticed in the photo's that I have the original T handle shifter setup on the trans. I was able to use the top parts of the original C3 handle and a piece of welding rod to adapt it to the ZF shifter and it even works the reverse lockout!

 

Congratulations. Beautiful work. However I share the concerns about the tailshaft being mounted to the crossmemer without any cushion. The engine/trans will move and something will break. (If you're lucky it will be something cheap). I would highly recommend installing a conventional transmission mount to allow for movement.

 

Should be able to buy a basic trans mount of about the right thickness and adapt it easily (shim if necessary). That would be my recommendation, also.